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joint

(joynt) [Fr. jointe, fr L. junctio, a joining] The place where two or more bones meet. Some joints are fixed or immobile attachments of bones; other joints allow the bones to move along each other. A joint usually has a thin, smooth articular cartilage on each bony surface and is enclosed by a joint capsule of fibrous connective tissue. A joint is classified as immovable (synarthrodial), slightly movable (amphiarthrodial), or freely movable (diarthrodial). A synarthrodial joint is one in which the two bones are separated only by an intervening membrane, such as the cranial sutures. An amphiarthrodial joint is one having a fibrocartilaginous disk between the bony surfaces (symphysis), such as the symphysis pubis; or one with a ligament uniting the two bones (syndesmosis), such as the tibiofibular articulation. A diarthrodial joint is one in which the adjoining bone ends are covered with a thin cartilaginous sheet and joined by a joint capsule lined by a synovial membrane, which secretes synovial fluid. SYN: SEE: arthrosis (1)

TYPES OF JOINTS

MOVEMENTJoints are also grouped according to their motion: ball-and-socket (enarthrodial); hinge (ginglymoid); condyloid; pivot (trochoid); gliding (arthrodial); and saddle.

Joints can move in four ways: gliding, in which one bony surface glides on another without angular or rotatory movement; angulation, occurring only between long bones, increasing or decreasing the angle between the bones; circumduction, occurring in joints composed of the head of a bone and an articular cavity, the long bone describing a series of circles, the whole forming a cone; and rotation, in which a bone moves about a central axis without moving from this axis. Angular movement, if it occurs forward, is called flexion; if backward, extension; if away from the body, abduction; and toward the median plane of the body, adduction.

Because of their location and constant use, joints are prone to stress, injury, and inflammation. The main diseases affecting the joints are rheumatic fever, rheumatoid arthritis, osteoarthritis, and gout. Injuries comprise contusions, sprains, dislocations, and penetrating wounds.

acromioclavicular joint

ABBR: AC joint A gliding or plane joint between the acromion and the acromial end of the clavicle.

movable joint

multiaxial joint

native joint

A natural joint present in the body without surgical modification as opposed to a prosthetic joint.

pivot joint

A joint that permits rotation of a bone, the joint being formed by a pivot-like process that turns within a ring, or by a ringlike structure that turns on a pivot. SYN: SEE: rotary joint; SEE: trochoid joint

plane joint

A synovial joint between bone surfaces, in which only gliding movements are possible.

synarthrodial joint

synovial joint

talocrural joint

tarsometatarsal joint

A joint composed of three arthrodial joints whose bones articulate with the bases of the metatarsal bones.

temporomandibular joint

Either of the encapsulated double synovial joints between the condylar processes of the mandible and the temporal bones of the cranium. These joints are separated by an articular disk and function as an upper gliding joint and a lower modified hinge or ginglymoid joint.